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This work provides a detailed analysis of a high efficiency Cu2ZnSnSe4 device using a combination of advanced electron microscopy and spectroscopy techniques. In particular, a full picture of the different defects present at the interfaces of the device and in the bulk of the absorber is achieved through the combination of high resolution electron microscopy techniques with Raman, X-ray fluorescence and Auger spectroscopy measurements at the macro, micro and nano scales. The simultaneous investigation of the bulk and the interfaces allows assessing the impact of the defects found in each part of the device on its performance. Despite a good crystalline quality and homogeneous composition in the bulk, this work reports, for the first time, direct evidence of twinning defects in the bulk, of micro and nano-voids at the back interface and of grain-to-grain non-uniformities and dislocation defects at the front interface. These, together with other issues observed such as strong absorber thickness variations and a bilayer structure with small grains at the bottom, are shown to be the main factors limiting the performance of CZTSe devices. These results open the way to the identification of new solutions to further developing the kesterite technology and pushing it towards higher performances. Moreover, this study provides an example of how the advanced characterization of emergent multilayer-based devices can be employed to elucidate their main limitations.

Energy transitions have placed the power system in the center of the energy agenda, since electricity constitutes a bridge between renewable resources and the decarbonization of the global economy. Therefore, due to stochasticity of renewable sources, guaranteeing a secure supply of electricity is crucial for achieving sustainable development, which has led energy security to become a priority within energy policy. This paper presents a review of four national security strategies focused in the power sector. The covered countries are the leaders in terms of electricity generation in their region, namely China, the United States, Germany and France, thus different approaches in the matter are contrasted and discussed. The analyzed countries tend to develop strategies focused on exploiting their indigenous energy resources. Nations possessing conventional fuels are willing to use them for enhancing their energy security under an all-of-the-above strategy, which implies also the expansion of renewable energy installations, as in the cases of the United States and China, while those ones that lack of fossil resources tend to compensate this hardship by relying deeper on renewable energy and reducing their energy consumption, as the European countries do. A frame for evaluating the effectiveness of these strategies on procuring energy security would be convenient for policy makers in order to strengthen security of the power sector.

Methods to obtain accurate estimations of the savings generated by building energy efficiency interventions are a topic of great importance, and considered to be one of the keys to increase capital investments in energy conservation strategies worldwide. In this study, a novel data-driven methodology is proposed for the measurement and verification of energy efficiency savings, with special focus on commercial buildings and facilities. The presented approach involves building use characterization by means of a clustering technique that allows to extract typical consumption profile patterns. These are then used, in combination with an innovative technique to evaluate the building’s weather dependency, to design a model able to provide accurate dynamic estimations of the achieved energy savings. The method was tested on synthetic datasets generated using the building energy simulation software EnergyPlus, as well as on monitoring data from real-world buildings. The results obtained with the proposed methodology were compared with the ones provided by applying the time-of-week-and-temperature (TOWT) model, showing up to 10% CV(RMSE) improvement, depending on the case in analysis. Furthermore, a comparison with the deterministic results provided by EnergyPlus showed that the median estimated savings error was always lower than 3% of the total reporting period consumption, with similar accuracy retained even when reducing the total training data available. This work was supported by the European Commission through the H2020 project SENSEI [grant number 847066]. The authors thank the Catalan Institute of Energy (ICAEN) for providing the monitoring and EEM data that was analysed in the case study.

Stand-alone electrification systems based on renewable energies are suitable for electrifying isolated rural communities. After some years of operation, their impact on the development of beneficiaries must be evaluated; in order to understand the strengths and weaknesses of each design option and to learn useful lessons for future projects. The literature lacks a unified study that compares the long-term impact on population of several projects combining different options for electricity generation (solar PV, wind and hydro) and distribution (microgrids and individual systems). In this context, this work performs a two-phase assessment of 9 electrification projects combining different systems and located in 6 rural Peruvian communities. First, a qualitative analysis is performed to monitor the progress experienced by the communities, considering previous evaluations carried out shortly after the projects’ implementation. Second, an in-depth analysis of the systems and the development of the communities is quantitatively performed through 28 indicators, evaluating 9 sustainability objectives organised into 4 dimensions: technical, social, economic and environmental. The results show that microgrid projects require and encourage community involvement to promote effective maintenance of the shared equipment. Conversely, individual systems can work for longer periods without as much regular maintenance, but still need an efficient management model to raise funds for repairs. Also, hydro is confirmed as providing continuous and high-quality supply, while solar and wind options allow more flexible designs. In all cases, a well-planned management model is essential for reducing the default rate, organizing effective maintenance and allowing the sustainable development of the community. Peer Reviewed Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.1 - Per a 2030, garantir l’accés universal a serveis d’energia assequibles, confiables i moderns Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energia Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.a - Per a 2030, augmentar la cooperació internacional per tal de facilitar l’accés a la investigació i a les tecnolo­gies energètiques no contaminants, incloses les fonts d’energia renovables, l’eficiència energètica i les tecnologies de combustibles fòssils avançades i menys contaminants, i promoure la inversió en infraestructures energètiques i tecnologies d’energia no contaminant Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.b - Per a 2030, ampliar la infraestructura i millorar la tecnologia per tal d’oferir serveis d’energia moderns i sos­tenibles per a tots els països en desenvolupament, en particular els països menys avançats, els petits estats insulars en desenvolupament i els països en desenvolupament sense litoral, d’acord amb els programes de suport respectius Objectius de Desenvolupament Sostenible::10 - Reducció de les Desigualtats Objectius de Desenvolupament Sostenible::10 - Reducció de les Desigualtats::10.2 - Per a 2030, potenciar i promoure la inclusió social, econòmica i política de totes les persones, independentment de l’edat, sexe, discapacitat, raça, ètnia, origen, religió, situació econòmica o altra condició

The market is searching for solutions to reduce emissions in the energy sector by increasing the consumer efficiency and flexibility and integrating renewable sources. Prosumers are suited to this role and are increasingly considered crucial to any such solution. Small-and-medium enterprises (SMEs) that need to upgrade their energy infrastructure, due to equipment obsolescence or external pressures to adopt greener echnologies, face difficulties in integrating new energy management strategies given the investment required and the payback periods. Industrial SMEs traditionally seek to make on-off investments with fast returns, exploiting the obtained equipment for its whole lifetime. Therefore, this paper presents a novel methodology to determine the optimal sizing and operation of the energy infrastructure for an industrial SME transitioning to a prosumer model to improve its economic perspectives, considering the exploitation of the infrastructure for its complete lifetime. The energy and economic profiles of SMEs are analysed and their energy infrastructure modelled in order to define the sizing and operation optimisation problem. Operation of the equipment is optimised considering weekly cycles along multiple years, obtaining the net present value of the investment. The proposed methodology, which employs direct search and linear programming techniques, enable industrial SMEs to undertake informed energy investment actions. A real manufacturing plant is described, characterized and used as the basis for a case study. The results show the economic feasibility of installing new energy equipment in SMEs, obtaining payback periods less than five years and final investment value of more than ten times the initial expense. Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura

This paper proposes a multi-objective hybrid energy management system that minimizes both the electricity expenses and the household greenhouse gas emissions released due to consumption, considering the entire life cycle of the generation assets used to provide energy. The global warming potential indicator is used to decide if it is more sustainable to purchase electricity from the grid or use the household’s flexible generation sources like photovoltaic panels and the energy storage system. Results prove that it is possible to reduce greenhouse gas emissions without incurring expensive electricity bill costs thanks to the hybrid-based home energy management system approach. This method gives the end-users a more influential role in the climate change solution, allowing them to give more or less importance to the economic or environmental component, according to their preferences.

Anomalous seasons such as extremely cold winters or low-wind summers can seriously disrupt renewable energy productivity and reliability. Better seasonal forecasts providing more accurate information tailored to stakeholder needs can help the renewable energy industry prepare for such extremes. The authors acknowledge funding from the EU Horizon 2020 project “Sub-seasonal to seasonal climate forecasting for energy (S2S4E)” (GA776787).

Electrical production for residential areas is one of the most important goals of SDGs (17 UN goal) and UN-Habitat III (14 goals) that can be achieved by renewable energy. Now, renewable energy is a significant issue that must be considered seriously as a policy and in order to achieve energy sustainability on a global scale especially in whole developing countries. Also, since the role of renewable energy in sustainable development is remarkable, thus this article presents a comprehensive discussion of energy sustainability for urban areas with related energy indicators and technical analysis of a Hybrid Power System to show the importance of renewable energy to gain energy sustainability. This paper presents the feasibility of using PV-DG hybrid systems as the reliable energy by an economic and technical analysis in one of the southern cities of Iran use of HOMER software. Regarding the high average of solar radiation that is about 5.4 kWh/m2/d in Chabahar city, technical analysis of this system demonstrates that this city has a high capacity to producing the electrical energy via PV-diesel hybrid system with total electrical production amount of 10,575 kWh/yr from PV (8,447 kWh/yr) and Diesel system (2,128 kWh/yr). For do this work at the first, the required data is gathered from the meteorological organization of Iran and then technical and economic analysis is conducted with the Homer software. This study regarding the high potential of solar energy of Chabahar city shows that to achieve development especially in the energy sustainability field needs to implementing proper actions such as enough investment on clean energy and using renewable energy for electrical production.

Hybrid photovoltaic-thermal (PVT) collectors have been proposed for the combined generation of electricity and heat from the same area. In order to predict accurately the electrical and thermal energy generation from hybrid PVT systems, it is necessary that both the steady-state and dynamic performance of the collectors is considered. This work focuses on the performance characterisation of non-concentrating PVT collectors under outdoor conditions. A novel aspect concerns the application of existing methods, adapted from relevant international standards for flat plate and evacuated tube solar-thermal collectors, to PVT collectors for which there is no formally established testing methodology at present. Three different types of PVT collector are tested, with a focus on the design parameters that affect their electrical and thermal performance during operation. Among other results, we show that a PVT collector suffers a 10% decrease in thermal efficiency when the electricity conversion is close to the maximum power point compared to open-circuit mode, and that a poor thermal contact between the PV laminate and the copper absorber can lead to a significant deterioration in thermal performance. The addition of a glass cover improves the thermal efficiency, but causes electrical performance losses that vary with the glass transmittance and the solar incidence angle. The reduction in electrical efficiency at large incidence angles is more significant than that due to elevated temperatures representative of water-heating applications. Dynamic performance is characterised by imposing a step change in irradiance in order to quantify the collector time constant and effective heat capacity. This paper demonstrates that PVT collectors are characterised by a slow thermal response in comparison to ordinary flat plate solar-thermal collectors, due to the additional thermal mass of the PV layer. A time constant of ∼ 8 min is measured for a commercial PVT module, compared to 2 min for a flat plate solar-thermal collector. It is also concluded that the use of a lumped, first-order dynamic model to represent the thermal mass of the PVT collector is not appropriate under certain irradiation regimes and may lead to inaccurate predictions of the system performance. This paper outlines a procedure for the testing and characterisation of solar collectors, provides valuable steady-state and dynamic performance characterisation data for various PVT collector designs, and also provides a framework for the application of this data in a system model to provide annual performance predictions in a range of geographical settings.

The high-penetration of Distributed Energy Resources (DER) in low voltage distribution grids, mainly photovoltaics (PV), might lead to overvoltage in the point of common coupling, thus, limiting the entrance of renewable sources to fulfill the requirements from the network operator. Volt-var is a common control function for DER power converters that is used to enhance the stability and reliability of the voltage in the distribution system. In this study, a centralized algorithm provides local volt-var control parameters to each PV inverter, which are based on the electrical grid characteristics. Because accurate information of grid characteristics is typically not available, the parametrization of the electrical grid is done using a local power meter data and a voltage sensitivity matrix. The algorithm has different optimization modes that take into account the minimization of voltage deviation and line current. To validate the effectiveness of the algorithm and its deployment in a real infrastructure, the solution has been tested in an experimental setup with PV emulators under laboratory conditions. The volt-var control algorithm successfully adapted its parameters based on grid topology and PV inverter characteristics, achieving a voltage reduction of up to 25% of the allowed voltage deviation. Peer Reviewed Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energia Objectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles Objectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles::11.6 - Per a 2030, reduir l’impacte ambiental negatiu per capita de les ciutats, amb especial atenció a la qualitat de l’aire, així com a la gestió dels residus municipals i d’altre tipus

In the last ten years, there has been a progressive improvement in rural electrification indexes in developing countries, and renewable energies are progressively being integrated into electrification programs. In Cuba, the government has set a target of 700 MW in solar photovoltaic energy by 2030, including rural electrification and off-grid systems. Within this framework, 10,000 modular systems of 300 Wp are being installed in isolated communities. Nowadays, previously diesel-electrified settlements are migrating into renewable energy technologies projects in rural Cuba. The objective of this research is to evaluate the sustainability of these changes in order to identify the implications for other developing countries, taking four different dimensions into account: environmental, technical, socioeconomic, and institutional. For this purpose, the rural communities of Yaguá (diesel-based) and Río Abajo (solar-based) in the province of Sancti Spiritus are visited and studied. Results show that the institutional dimension of sustainability is positive thanks to improvements in energy security and promotion of the Cuban national plan goals. Moreover, results confirm that the energy transition from diesel-based to solar PV is environmentally sustainable in Cuba, but improvements are still necessary in the power capacity of solar modules to strengthen the socioeconomic and technical dimensions.

It is a fact that electric vehicles (EVs) are beneficial for climate protection. However, the current challenge is to decide on whether to reuse an EV battery or to recycle it after its first use. This paper theoretically investigates these areas i.e., recycle and reuse. It was found that there are several commercially used recycling processes and also some are under research to regain maximum possible materials and quantity. The concept of reusing (second life) of the battery is promising because, at the end of the first life, batteries from EVs can be used in several applications such as storing energy generated from renewable sources to support the government grid. However, the cost and life-cycle analysis (LCA) demonstrated that there are several aspects involved in battery reuse applications. Henceforth, one LCA generalised method cannot provide an optimal approach for all cases. It is important to have a detailed study on each of the battery reusing applications. Until then, it is safe to say that reusing the battery is a good option as it would give some time to recycling companies to develop cost and energy-efficient methods. Peer Reviewed Objectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles::11.6 - Per a 2030, reduir l’impacte ambiental negatiu per capita de les ciutats, amb especial atenció a la qualitat de l’aire, així com a la gestió dels residus municipals i d’altre tipus Objectius de Desenvolupament Sostenible::12 - Producció i Consum Responsables Objectius de Desenvolupament Sostenible::12 - Producció i Consum Responsables::12.2 - Per a 2030, assolir la gestió sostenible i l’ús eficient dels recursos naturals Objectius de Desenvolupament Sostenible::12 - Producció i Consum Responsables::12.4 - Per a 2020, aconseguir la gestió ecològicament racional dels productes químics i de tots els residus al llarg del seu cicle de vida, de conformitat amb els marcs internacionals convinguts, i reduir-ne de manera significativa l’alliberament a l’atmosfera, a l’aigua i al sòl a fi de minimitzar-ne els efectes adversos sobre la salut humana i el medi ambient Objectius de Desenvolupament Sostenible::12 - Producció i Consum Responsables::12.5 - Per a 2030, disminuir de manera substancial la generació de residus mitjançant polítiques de prevenció, reducció, reciclatge i reutilització Objectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles

Nowadays, distributed energy sources are widely used to supply demand in micro grids (MGs) especially in the green buildings. Despite increasing number of intermittent distributed energy resources, MGs have essential influence on decreasing use of conventional generation, but it give rise to new challenges in terms of energy management, stability and reliability of system. Multi-agent systems (MASs) as distributed smart units have been widely used recently. However, control and implementation of these smart structures enhance existing challenges because these units need a framework that, at first, guarantees operation of MASs and then insures management in generation and demand side. This paper presents a smart control and energy management of a DC microgrid that split the demand among several generators. An energy management system (EMS) based on multi-agent system (MAS) controller is developed to manage energy, control the voltage and create balance between supply and demand in the system with the aim of supporting reliability characteristic. In the proposed approach, a self-healing hierarchical algorithm is implemented to control interaction of agents and also guarantees reliability of smart control system under faults. Theoretical analysis and simulation results for a practical model demonstrate that the proposed technique provides a robust and stable control of a microgrid.

This work reports the design, manufacturing and catalytic activity characterization of a micro-reformer for hydrogen-rich gas generation integrated in portable-solid oxide fuel cells (μ-SOFCs). The reformer has been designed as a silicon micro monolithic substrate compatible with the mainstream microelectronics fabrication technologies ensuring a cost-effective high reproducibility and reliability. Design and geometry of the system have been optimized comparing with the previous design, consisting in an array of more than 7x103 vertical through-silicon micro channels perfectly aligned (50 μm diameter) and a 5 W integrated serpentine heater consisting of three stacked metallic layers (TiW, W and Au) for perfect adhesion and passivation. Traditional fuels for SOFCs, such as ethanol or methanol, have been replaced by dimethyl ether (DME) and the chosen catalyst for DME conversion consists of Pd nanoparticles grafted on an alumina active support. The micro-channels have been coated by atomic layer deposition (ALD) with amorphous Al2O3 and the influence of rapid thermal processing (RTP) on such film has been studied. A customized ceramic 3D-printed holder has been designed to measure the specific hydrogen production rates, DME conversion and selectivity profiles of such catalyst at different temperatures.

This paper will provide a classification of high efficiency switching power-gyrator structures and their use as cells for energy processing in photovoltaic solar facilities. Having into account the properties of these topologies presented in the article, their inclusion in solar facilities allows increasing the performance of the whole installation. Therefore, the design, simulation and implementation of a Gtype power gyrator are carried out throughout the text. In addition, in order to obtain the maximum power from the photovoltaic solar panel, a maximum power point tracking (MPPT) is mandatory in the energy processing path. Therefore, the practical implementation carried out includes a control loop of the power gyrator in order to track the aforementioned maximum power point of the photovoltaic solar panel.

This paper analyses a novel countermeasure to Leakage Power Analysis Attacks based on the application of a random Body Bias voltage level at the beginning of the encryption process. The countermeasure effectiveness is established through the development of a theoretical model of the Pearson correlation coefficient in the presence of a varying body bias under both noiseless assumptions and in the presence of algorithmic noise, and through simulations on a partial cryptosystem implemented in 28 nm FDSOI technology. A study of the effect of averaging power measurements is also developed and contrasted against Monte Carlo simulations of the countermeasure scheme, effectively providing a floor for the increase in required measurements to identify the secret key.

Biomass-based, small-scale Combined Cooling, Heating and Power (CCHP) systems can increase the energy autonomy of building complexes while reducing their Greenhouse Gases (GHG) emissions. In combination with air-to-water Heat Pumps (HP), highly efficient energy systems can be designed, which allow for high flexibility in serving thermal and electric demands. This study presents an exergy evaluation of such a small-scale CCHP/HP system using a dynamic modelling approach based on gasification of various types of woody biomass. The transient model takes into account the effects of the biomass chemical composition as well as of ambient temperatures on the exergy performance of all key components for various CCHP system sizes supporting an HP system. The model has been applied in a case study for a historic building complex, where the CCHP sub-system would support an HP-subsystem allowing for downsizing the latter. The results show that smaller CCHP systems operate with higher exergy efficiency, because for larger systems the heat transfer from the engine and the operation of the absorption chiller are less exergy efficient. The electric load-following CCHP subsystem reaches exergy efficiencies of up to 13.3%, indicating huge improvement potential for system and sub-system design. It was also found that the biomass composition heavily influences the exergy efficiency of the gasifier and in turn changes the exergy efficiency of the syngas engine and the entire CCHP sub-system. Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant Objectius de Desenvolupament Sostenible::12 - Producció i Consum Responsables Objectius de Desenvolupament Sostenible::13 - Acció per al Clima

This paper presents a proposal for potential bioelectrochemical power to gas stations. It consists of a two-level voltage source converter interfacing the electrical grid on the AC side and an electromethanogenesis based bioelectrochemical system (EMG-BES) working as a stacked module on the DC side. The proposed system converts CO2 and electrical energy into methane, using wastewater as the additional chemical energy input. This energy storage system can contribute to dampening the variability of renewables in the electrical network, provide even flexibility and grid services by controlling the active and reactive power exchanged and is an interesting alternative technology in the market of energy storage for big energy applications. The big challenge for controlling this system lays in the fact that the DC bus voltage of the converter has to be changed in order to regulate the exchanged active power with the grid. This paper presents a cascade approach to control such a system by means of combining external control loops with fast inner loops. The outer power loop, with a proportional-integral (PI) controller with special limitation values and anti-windup capability, is used to generate DC bus voltage reference. An intermediate loop is used for DC bus voltage regulation and current reference generation. A new proportional resonant controller is used to track the current reference. The proposed scheme has been validated through realtime simulation in OPAL OP4510. This research was funded by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie, grant number 712949 and the Spanish Ministry of Economy and Competitiveness under the project RTI2018-100921-B-C21.

Series connections of modules in cascaded multilevel converters are prone to power imbalances due to voltage differences on their DC side. When modules are connected to direct current (DC) sources, such as photovoltaic panels, the capability of withstanding power imbalances is crucial for generating the maximum power. In order to provide a possible solution for this requirement, this paper proposes a control strategy called Quadrature Voltage Compensation, which allows a wide range of power imbalances. The proposed control strategy regulates the power by introducing a circulating current between the arms and a phase angle in the output voltage. The impact of the circulating current and its effect on the phase voltage are studied. To highlight the features of the proposed strategy, an analytical model based on vector superposition is also described, demonstrating the strong capability of tolerating power differences. Finally, to validate the effectiveness of the Quadrature Voltage Compensation, simulation and experimental results are presented for a three-phase isolated multi-modular converter. This work was supported by the Ministry of Science Innovation and Universities under the project RTI-2018-100921-B-21 and by the European Commission under the projects FLEXITRANSTORE H2020-LCE-2016-2017-SGS-774407 and INTERRFACE H2020-LC-SC3-2018-ES-SCC-824330.

The advent of renewable energy has posed difficulties in the operation of power systems whose net inertia is becoming critically low. To face such challenges, grid-forming power has been one of the potential solutions pursued by the industry and research community. Although promising, grid-forming power converters are still immature for mass deployment in power systems. In the meanwhile, an enormous amount of grid-following power converters has been underexploited when it comes to grid-supporting functionalities. Therefore, this article proposes an external inertia emulation controller (eIEC) for grid-following power converter to provide frequency support to the grid. For the purpose of minimizing installation efforts and resources, the controller is designed in such a way that it can be implemented in an external controller communicating with the grid-following power converter via an industrial communication link. This article also investigates the effect of communication delay on the stability performance of the proposed controller. In addition to the detailed analysis, hardware-in-the-loop experiments are also carried out to validate the proposed eIEC. This work was supported by the European Commission under Project FLEXITRANSTORE-H2020-LCE-2016-2017-SGS-774407

19th International Conference on Renewable Energies and Power Quality (ICREPQ’21) Almeria (Spain), 28th to 30th July 2021 Photovoltaic power generation systems are one of the main renewable power sources, and quasi-Z-source inverters are becoming powerful devices to integrate these systems in AC grids. However, stability issues due to the damping behaviour of converters must be considered. There are several studies in this direction but instability concerns are not completely solved yet. This paper contributes with a procedure for the stability assessment of photovoltaic power generation systems with quasiZ-source inverters in the frequency domain. The study is based on the small-signal averaged model of the system expressed in the s-domain and the stability criterion derived from the frequency characteristics of the state-space matrix. The influence of the photovoltaic power generation system operating point on stability is studied by the proposed procedure. Eigenvalue analysis and PSCAD/EMTDC simulations are also performed to validate the obtained results.

9 pags., 7 figs., 2 tabs., Semi-transparent solar cells are the next step for photovoltaics into our daily life. Over the last years, kesterite-type material has attracted a special attention to be used as an absorber in thin-film solar cells because of its low toxicity and earth abundant constituents. Here, Cu2ZnGeSe4 (CZGSe) thin films are grown by co-evaporation and subsequent annealing at a maximum temperature of 480 ◦C or 525 ◦C onto Mo/V2O5/FTO/glass stacks. The goal of this work is to investigate the influence of the annealing temperature on the composition, morphology, vibrational properties, and transmittance of CZGSe layers, the formation of secondary phases, and distribution of elements within the absorber layer as well as on the optoelectronic properties of the corresponding solar cell devices. Raising the annealing temperature to 525 ◦C leads to a more uniform distribution of Cu, Zn, Ge and Se throughout the absorber layer, a reduction of the presence of the GeSe2 secondary phase, which is mainly detected at 480 ◦C, a larger grain size and the formation of a thicker MoSe2 layer at the CZGSe/back contact interface. The strategy of increasing the annealing temperature allows for improved J–V characteristics and higher spectral response resulting in an enhanced device performance of 5.3% compared to 4.2% when using 525 ◦C and 480 ◦C, respectively. Both absorber layers present an optical band gap energy of 1.47 eV. Furthermore, higher annealing temperature has beneficial effect to the CZGSe-based devices without losses in total transmitted light because of the higher diffuse transmittance. This work shows first promising semi-transparent CZGSe-based solar cells possibly open up new routes of applications., This work was supported by Spanish Ministry of Science, Innovation and Universities Project WINCOST (ENE2016-80788-C5-2-R), Project RTI (2018-096498-B-I00, AEI/MICINN/ERDF) and European Project INFINITE CELL (H2020-MSCA-RISE-2017-777968). Authors from IREC belong to the SEMS (Solar EnergyMaterials and Systems) Consolidated Research Group of the ‘Generalitat de Catalunya’ (Ref 2017 SGR 862).MG and MP acknowledge the financial support from Spanish Ministry of Science, Innovation and Universities within the Juan de la Cierva (IJC2018-038199-I) and Ramón y Cajal (RYC-2017-23758) Fellowships respectively. MGP also acknowledges funding from AEI/MICINN (PTA2019-016763-I). The authors acknowledge the service from the MiNa Laboratory at IMN-CSIC, and funding from CM (project S2018/NMT-4291 TEC2SPACE), MINECO (project CSIC13-4E-1794) and European Union (FEDER, FSE).

In photovoltaic (PV) systems, the reliability of the system components, especially the power converters, is a major concern in obtaining cost effective solutions. In order to guarantee service continuity in the case of failure of elements of the PV converter, in particular, semiconductor switching devices, a solution is to design power converter with fault-tolerance capability. This can be realized by aggregating hardware redundancy on an existing converter, providing the possibility of replacement of faulty elements. This paper evaluates the reliability of a fault-tolerant power electronics converter for PV multistring application. The considered fault-tolerant design includes a single redundant switching leg, which is used in order to reconfigure the structure in case of a switch failure either on DC-AC or DC-DC stages. This paper details the reliability estimation of the considered PV multistring fault-tolerant converter. Furthermore, a comparison with a conventional structure without fault-tolerant capability is provided. The results show that the introduction of a single redundant leg allows for improving the converter mean time to failure by a factor of almost two and it reduces, by half, the power loss due to system-failure shutdowns in PV applications, while only increasing the converter cost by 2–3%.

The number of people living in nursing homes is increasing due to the growth of ageing population. However, existing standards on thermal comfort do not consider how occupants of nursing homes perceive their thermal environment. This study investigated the thermal sensation of elderly people during summer season in care homes from the Mediterranean climate. The study was conducted to 623 nursing occupants (both residents (elderly people) and non-residents (caregivers)) using a thermal sensation questionnaire and measurement of indoor climatic parameters. Elderly’s results were compared with the results of caregivers to study the differences between these groups of population that coexist in the same building. The results showed that elderly people have a different thermal comfort perception than adults. The comfort temperature for elderly people was found to be 24.4ºC while for non-elderly was 23.5ºC while residents were found to be more tolerant with high temperatures than non-residents. Results also showed that residents do not modify the clothing to adapt to unsatisfactory thermally conditions or to the activity. The results of this research may assist regulatory bodies to develop guidelines to design and operate nursing homes based on real thermal needs of their occupants. The authors thank the Programa de Cooperación Interreg V-AEspaña – Portugal, (POCTEP) 2014-2020 and the FEDER funds fortheir financial support to this study under the project reference6/2018_CIE_6. We would also like to thank Sanitas Mayores andspecially the Eng. Marc Vallet for providing their nursing homesand helping collecting all the required data. We would also liketo extend our appreciation to all the caregivers, maintenance staffand elders who participated in this project.

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works Big data analysis is becoming an increasing field of interest for research to analyse, identify and predict final user’s behaviour. For this reason, in the energy sector, smart metering is generally used to find new business opportunities and, theoretically, it is said that it could also help to fight energy poverty issues. Nonetheless, when tackling social injustice issues, the deployment of massive technology might also bring other side effects. This study analyses the capability of smart metering to mitigate energy poverty in Europe according to the current approaches of projects and the risks it might bring to the more vulnerable layers of our society.

In this research, the modeling, simulation, and analysis of the energy conversion equations that describe the behavior of a hybrid photovoltaic and wind turbine system that supplies electrical energy to an average organic architecture is performed. Organic constructions have a philosophy that seeks to understand and integrate into the site, taking advantage of the natural potentials and their resources of the surrounding areas so that they form part of a unified and correlated composition. The rooms in these buildings are designed similar to a bean, inspired by the uterus of a mother and her child who are comfortable, at rest, and alive. We are left with the task of spreading this research to integrate its energy potential from the surroundings and transform it into autonomous electrical energy. In this article, a numerical model based on the fundamental equations was developed and coded, and the results compared with experimental data with a real airplane-type system located in a remote area of Ecuador. The model is intended to be used as an optimization and design tool for such hybrid systems applied to organic constructions. After an error analysis it was determined that this model predicted quite interesting results compared to the experimental data under various conditions. It is important to indicate that this analysis has been carried out so that in the future, these power generation systems can be exploited and applied more efficiently in areas far from the public electricity grid.

Worldwide electricity generation is featured by the growth of intermittent renewable energies. In this context, hydropower plays a fundamental role because it provides flexibility to the power grid and ensures its stability. The new grid requirements have led hydropower units to working under a wider range of loads and with more start/stop sequences. Pelton turbines are the most suitable for high heads and have a large regulation capacity. In operation, the runner is impinged by high-speed water jets, and, thus, subjected to strong pulsating forces. As a consequence, the structure presents large deformations and high stresses, especially on the buckets. This situation can be much aggravated if the frequency and shape of the excitation is resonant with those of the structure. Therefore, the modal response of the turbine must be thoroughly studied and the most dangerous frequencies avoided. In this paper, a detailed analysis of the modal behavior of Pelton turbines is presented. Four prototypes have been studied for such purpose. The first one has been modeled numerically and analyzed experimentally. Following a systematic investigation, the effect on the modal shapes and the frequencies of the different parts comprising the turbine has been evaluated. The single bucket and the whole runner have been studied. Finally, another turbine installed in the same power plant has been analyzed to determine the effect of the mechanical design on the frequencies. In addition, two prototypes belonging to other power plants have been studied to see the effects of the hydrodynamic design on the modal behavior.

The possibility for harnessing energy from thermal or concentration gradients by the use of ducts lined with hydrophobic microcavities is discussed. Utilizing a physical and simplified model an expression for the attainable pumping power was derived.

Solar and wind can be considered as sustainable environmentally friendly and omnipresent renewable energy sources for generating a part of required electrical energy for inhabitants of the remote areas in different countries. Accordingly, this study investigates the techno-economic evaluation for two-hybrid renewable energy systems for Bandar Dayyer. The findings of this study shows that using the HOMER software, the total amount of electricity production by these systems are equal to 470,176¿kW, of which 22,409¿kW is provided by PV-generic system and 447,767¿kW is supplied by PV-diesel-generic system. It should be mentioned that this area has an appropriate potential of wind speed and solar radiation; therefore, the area can be suitable for investing on a hybrid renewable energy site.

Electric vehicles (EVs) are considered a viable alternative to internal combustion engine vehicles (ICEVs) and as a result of recent advances in battery technologies, sales are increasing year by year. However, recycling these batteries at the end of their useful life in the car can be a problem because they contain materials that can harm human health and the environment. Thus, car manufacturers consider that when those batteries have finished their first life in an EV, they still contain enough energy and capacity to be used in a stationary energy storage systems (SESSs), significantly contributing towards an increased sustainable transport sector in the future. This study focuses the analysis on the viability of a SESS installation, considering battery ageing from an economic perspective in two different real scenarios in Spain. This study simulates the electricity bill cost with and without SESS and calculates the annual savings accordingly. Following, the return on investment (ROI) of installing a SESS is calculated. Afterwards the lifetime of the batteries is calculated in order to compare it with the ROI and to decide if the installation of a SESS is advisable from an economic point of view. Major results indicate that any feasibility study of installing a SESS must be studied from an economic and battery ageing point of view.

The following paper aims to prove the importance of embedding the regulatory framework when analyzing the distributed generation activity of an energy community. At present, most of the scientific literature has focused on distributed energy, and energy communities address the issue of regulatory frameworks qualitatively. In this paper, the most representative regulatory frameworks devoted to the promotion of energy communities were analyzed and synthesized, namely, feed-in tariffs, net metering, and the self-consumption scheme. As a result, an algebraic model able to represent the essence of the regulatory structures related to those remuneration mechanisms was obtained. Next, this model was embedded into a physical model, based on real data, previously created. The resulting Mixed Integer Linear Program (MILP) was used to identify the implications of these frameworks. The results demonstrate the impact of regulatory schemes on energy management and economic results of an energy community. Indeed, profitability changes drastically depending on which remuneration scheme is applied to an energy community.

The electricity sector foresees a significant change in the way energy is generated and distributed in the coming years. With the increasing penetration of renewable energy sources, smart algorithms can determine the difference about how and when energy is produced or consumed by residential districts. However, managing and implementing energy demand response, in particular energy flexibility activations, in real case studies still presents issues to be solved. This study, within the framework of the European project “SABINA H2020”, addresses the development of a multi-level optimization algorithm that has been tested in a semi-virtual real-time configuration. Results from a two-day test show the potential of building’s flexibility and highlight its complexity. Results show how the first level algorithm goal to reduce the energy injected to the grid is accomplished as well as the energy consumption shift from nighttime to daytime hours. As conclusion, the study demonstrates the feasibility of such kind of configurations and puts the basis for real test site implementation.

Hydropower is nowadays essential for balancing the electrical grid providing flexibility and fast response. The role of hydraulic turbines has changed from working at their Best Efficiency Point (BEP) to work in the whole operating range when demanded. Francis turbines working at off-design conditions suffer from dynamic problems that affect the useful life of their components, especially of the runner. Reduced scale physical models of Francis turbines are widely used to determine their hydraulic behavior. Most of the hydraulic parameters obtained in model tests are transposable to prototype by using the similarity theories as long as they meet similitude requirements. However, from the mechanical behavior point of view, both model and prototype structures are not always similar and the mechanical behavior of the model is often not considered for transposition. In this paper, a transposition method for the mechanical behavior of Francis turbines models is presented and the results are compared with the real size prototype. The modal behavior of the runner, its stress and fatigue life estimation for different operating conditions are experimentally compared for both model and prototype. Results present the possibilities and limitations of transposing the mechanical parameters from model to prototype.

This work aims to unveil the optimal annealing conditions and surface treatments of CZGeSe absorbers, synthesized using vacuum-based deposition technique, with an eye to optimizing the main parameters allowing better control of secondary phases formation and improving crystalline quality of this absorber. Firstly, a comparative study is given of one and two-step annealing profiles, where, for each thermal treatment, the optimal temperature is probed. The second section of this study underlines the evaluation of the surface treatment effect on the as-annealed absorber using different etching agents. Finally, the effect of different post-annealing treatment temperatures on the overall performance of the fabricated devices is evaluated. For the studied optimizations, a deep understanding of the cell behavior is provided through structural, morphological and electrical characterizations. Preliminary results have given an efficiency up to 5.6% with higher Voc = 572 mV and FF = 65% compared to the reported record cell using similar absorber (Voc = 558 mV, FF = 59%). This performance is linked to the implementation of a two-step annealing process with lower temperatures (330 °C/480 °C) as it showed the best crystallinity-efficiency trade-off along with the smallest amount of ZnSe secondary phase among all the thermal routines studied. In addition, after the evaluation of several etching agents, the implementation of a KCN etching has shown to be the most effective leading to a remarkable improvement of the PN junction through a surface passivation.

Research towards renewable energy sources is of great relevance in the pursue of environmental impact reduction and to decrease the dependency on fossil fuels. In high solar irradiation locations, the use of Concentrating Solar Power technologies might be a good alternative in front of other power sources. This study presents how multi-criteria methods such as the weighted technical analysis are useful to select the best heat transfer fluid to be used in a relatively small Concentration Solar Power plant in the Burkina Faso. To do so it analyzes three aspects, the technical performance of thermal fluids, their environmental impact and their price, giving them different weights to confer more or less relevance according to the idiosyncrasy of the region. To do the technical analysis, this study simulates the heat gain and temperature increase of four heat transfer fluids while passing through a solar parabolic trough. The environmental impact factor is evaluated following the life cycle assessment methodology and the economic factor compares their price in the market. Results show that Dowtherm A is the best choice for Burkina Faso and Marlotherm is the worst, but these results change considerably if the comparison is done in the USA, where the environmental factor gains relevance in contrast to the economic factor.

This study presents a method to analyse the secure and optimal operation of transmission systems consisting of both HVDC (high-voltage direct current) and high-voltage alternating current interconnections under a scenario of high penetration of offshore wind and taking into account the system spinning reserves. Different reliability management strategies are assumed, accounting for a single AC element and/or a single DC element outage and taking into consideration the probability of failure of the different power system components. The cost of operation of the system and the wind energy curtailed over the operating time are determined. This method is applied to a study case, based on the CIGRÉ HVDC Test System. The system behaviour over a complete year is modelled using realistic wind generation and demand based on scaling data from the Belgian power system.

Currently, around 1.1 billion people lack access to electricity, mainly in developing countries. Solar photovoltaic systems can provide electricity, but the design is complex, having to size and site the equipment. Besides, since forecasting consumption habits for newly electrified populations is complex, the estimation of the electricity needs is uncertain. This work addresses, for the first time, demand uncertainty to assist promoters in designing electricity access projects, simultaneously solving the sizing and siting problems, using fuzzy logic. In particular, a mathematical model is proposed, introducing uncertainty through five modelling approaches with different fuzzy logic assumptions: three based on the literature and two novel ones according to the conflicting problem nature (project cost minimisation vs electricity supply maximisation). The five approaches are compared and the new ones obtain solutions achieving a higher satisfaction regarding the cost and electricity supply. Then, the most efficient approach is applied in two Peruvian communities, comparing the solutions with those obtained without uncertainty. The results of the proposal show a better balance between the project cost and the demand supplied. Hence, the proposal can help promoters in developing countries to better design electricity access projects where the demand estimation is complex.

This article proposes a methodology to assess building behaviour, whilst taking its life cycle into account. Understanding of the system can be obtained by combining well-known energy consumption calculation engines (TRNSYS) with co-simulation processes defined using Specification and Description Language (SDL). In this instance, to find the best comfort, energy and cost scenarios for energy rehabilitation, Co-simulation is conducted in two phases: the best scenes of passive systems are found, those presented as a priority; and, the active systems are made with ‘brute force analysis’. The article provides the results for a case study: a single-family home built between 1991 and 2007 and located in Mediterranean climate zone. The methodology provides a set of passive energy efficiency measures, to improve until two scales in the building energy labelling system. Using the methodology and the proposed model has enabled us to dramatically reduce the run time until 75% and therefore.

The three phase induction machine is used in the mainly part of the industry and it requires reactive power from the grid to start and function. The reactive power consumption is economically fined so the industries install capacitors in parallel with the motors and loads. The bank capacitor, gives this reactive power to the machine in order to improve the cos f factor in the installation. When a fault appears in the grid, this machine gives the active power to the fault, but when the overcurrent relay sets the fault, the induction machine is already with inertia with electromagnetic and mechanic specific parameters that originate a non-controlled islanding mode and it provides the power to the loads on this feeder. Even though several works are published within the islanding detection, the islanding operation about the induction machine as a generator in power wind energy applications, nevertheless in the following we show the motor perspective. The stability of the system in the time period between the relay opening and the fast reconnection is out of control, so a complete study a about the electric magnitudes, voltage and reactive power , active power and frequency and the angle stability is needed. In this paper we show a real case that appears in a distribution Medium Voltage (MV) radial network in Spain in a 25 kV feeder and we summarize the voltage /current wave form and the frequency oscillation.

As it is well known, the Bologna Process is a voluntary intergovernmental European cooperation initiative that led to the creation of the named European Higher Education Area (EHEA). EHEA was formed to promote mobility, increase academic recognition and attract students and staff from around the world to Europe. On the other hand, since September 2016, the Technical University of Catalonia (Universitat Politècnica de Catalunya, UPC) – BarcelonaTech has a new Campus in Barcelona City, the Diagonal-Besòs Campus. In this new Campus appears the Eastern Barcelona School of Engineering (Escola d’Enginyeria de Barcelona Est, EEBE), with new Bachelor’s and Master’s Degrees. In this framework, also since September 2016, the EEBE is offering the new 4-year Bachelor’s Degree in Energy Engineering with a total number of 240 ECTS credits. Current article deals with the inclusion of the course about sizing and design of renewable energy systems in the context of this degree. In particular, and although this topic was eventually abandoned in the initial degree curriculum, the paper presents the development of a 3rd-year course, Renewable Energies, that focuses on this topic.

The conversion of carbon dioxide (CO2) into value-added chemicals and fuels, preferably using renewable energy and earth-abundant materials, is considered a key priority for future energy research. In this work, a bias-free reactor device for the solar-driven conversion of CO2 to synthesis gas (syngas) has been developed. The integrated fluidic device consists of a cathode made of copper foam coated with low-cost nanosized zinc flakes as catalyst to perform the CO2 reduction reaction (CO2RR) to syngas, an adapted silicon heterojunction solar cell structure as photoanode with nickel foam as catalyst to facilitate the oxygen evolution reaction (OER), and a bipolar membrane separating the respective catholyte and anolyte compartments. The membrane allows for the operation of the catholyte and anolyte at different pH values. Stable and tunable hydrogen-to-carbon monoxide (H2 : CO) ratios between 5 and 0.5 along with high CO Faradaic efficiencies of up to 85% and CO current densities of 39.4 mA cm−2 have been demonstrated. Under photoelectrolysis conditions, the photovoltage of the photoanode was varied between 0.6 V and 2.4 V by connecting up to four heterojunction solar cells in series, and thus reducing the overall cell voltage solely by solar energy utilization. Bias-free operation of the integrated device has been achieved under ambient conditions with active areas for CO2RR and OER, respectively, of 10 cm2. An operation current density of 5.0 mA cm−2 was measured under 100 mW cm−2 illumination of the complete device, which corresponds to a solar-to-syngas conversion efficiency of 4.3%.

Integration of renewable energy sources in the electrical power system is key for enabling the decarbonization of that system [...]

As new grid codes have been created to permit the integration of large scale photovoltaic power plants into the transmission system, the enhancement of the local control of the photovoltaic (PV) generators is necessary. Thus, the objective of this paper is to present a local controller of active and reactive power to comply the new requirements asked by the transmission system operators despite the variation of ambient conditions without using extra devices. For this purpose, the control considers the instantaneous capability curves of the PV generator which vary due to the change of solar irradiance, temperature, dc voltage and modulation index. To validate the control, the PV generator is modeled in DIgSILENT PowerFactory ® and tested under different ambient conditions. The results show that the control developed can modify the active and reactive power delivered to the desired value at different solar irradiance and temperature.

Since the depletion of fossil energy sources, rising energy prices, and governmental regulation restrictions, the current manufacturing industry is shifting towards more efficient and sustainable systems. This transformation has promoted the identification of energy saving opportunities and the development of new technologies and strategies oriented to improve the energy efficiency of such systems. This paper outlines and discusses most of the research reported during the last decade regarding energy efficiency in manufacturing systems, the current technologies and strategies to improve that efficiency, identifying and remarking those related to the design of management/control strategies. Based on this fact, this paper aims to provide a review of strategies for reducing energy consumption and optimizing the use of resources within a plant into the context of discrete manufacturing. The review performed concerning the current context of manufacturing systems, control systems implemented, and their transformation towards Industry 4.0 might be useful in both the academic and industrial dimension to identify trends and critical points and suggest further research lines.

The renewed concern for the care of the environment has led to lower emissions of greenhouse gases without sacrificing modern comforts. Widespread proposal focuses on energy produced from renewable sources and its subsequent storage and transportation based on hydrogen. Currently, this gas applies to the chemical industry and its production is based on fossil fuels. The introduction of this energy vector requires the development of environmental-friendly methods for obtaining it. In this paper, existing techniques are just presented and the main focus is made on electrolysis, a mature procedure. In turn, some developed proposals as previous steps to the hydrogen economy are presented. Finally, some lines of research to improve alkaline electrolysis technology are commented. Fil: David, Martín Rafael. Instituto Tecnológico de Buenos Aires; Argentina. Universidad Politécnica de Catalunya; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Ocampo Martínez, Carlos. Universidad Politécnica de Catalunya; España Fil: Sanchez Peña, Ricardo Salvador. Instituto Tecnológico de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Oscillating water column (OWC) axial impulse turbines permit the conversion of wave energy into electrical power. Unlike other hydropower units with a mature and well established technology, such turbines have been recently developed, there are still few prototypes operating and therefore there is a large space for optimizing its design. Many recent studies focus on the improvement of the efficiency and transient characteristics by means of experimentation and also simulation techniques. In the present paper we use a 3D numerical simulation model (computational fluid dynamics model with ANSYS-Fluent 18) to analyze the influence of different geometrical parameters on the efficiency of the turbine, which have been less discussed yet. A reference configuration case has been used to validate our simulation model by comparing it with previous experimental results. Then, parametric variations in the guide vane number and type, gaps between the rotating and stationary part and hub to tip ratio have been introduced in the model to discuss the influence of these effects. It is found that some of these parameters have an important influence on the efficiency of the turbine and therefore, the results presented in this paper can help to optimize future designs of OWC impulse turbines.

The electric vehicle is presented as an environmental friendly alternative to common vehicles and as the future of transportation. However, car manufacturers consider that electric vehicle batteries are not useful for traction purposes when they reach a state of health of 80%. Thus, as a matter of fact, these batteries are sold knowing that they have a premature obsolescence, as they still have 80% of useful capacity that could be used elsewhere. This study analyzes economically and in terms of ageing performance the possibility to provide a second life to these batteries in buildings. The study presents several scenarios depending on the battery use, considering independent buildings or getting closer to the concept of smart grid with demand response services where buildings could participate in secondary electricity markets by means of an energy aggregator. Moreover, the study analyzes the existing European markets that allow aggregated demand response services. Results show that, effectively, the reuse of batteries for residential purposes might not be the best economical option even though their lifespan is enlarged four years more. Nonetheless, if they are able to participate in secondary electricity markets in addition to their normal use in buildings, the business becomes juicy enough having a relatively low impact on ageing. The promotion of electric vehicle battery reuse is necessary, as there is a large amount of batteries with a huge useful potential in stationary applications coming in the nearby future from the electric vehicles that have been sold during the last five years. If possible, car manufacturers should consider eco-design in order to facilitate this battery repurposing and lifespan enlargement.

The objective of this paper is to propose a simple approach to solve the steady state of a wind turbine (WT) equipped with a doubly-fed induction generator (DFIG) which can be used to initialize dynamic studies of the machine. The idea is to model the rotor-side converter (RSC) as a constant current source connected to the rotor of the DFIG. The resulting equivalent circuit consists of a voltage source in series with a reactance, which makes it possible to obtain simple phasor expressions that can be used to obtain the Park components of the variables. The proposed method is compared with the traditional Newton-Raphson algorithm, showing that it is easier and faster to implement, as it makes use of the phasor expressions and it does not require an iterative process to obtain the final solution. Finally, the results of the proposed method are used to simulate a 2 MW DFIG-based WT under three-phase faults, considering three different WT operating points. In these simulations, the idea of constant rotor current is extrapolated to the entire event. The simulated results show that both current at torque peaks are reduced. The analytical study and the simulations have been carried out in MATLAB.

As a contribution to the study of the urban energy transition, this paper proposes a novel model of energy-economic evaluation of the cities self-sufficiency and presents its application in the form of a case study. The objective of this study was to analyse the scope of the investment in the photovoltaic self-consumption of buildings in order to promote the creation of Prosumers communities within the cities. The operation of this model is based on the scalability of the Nearly Zero Energy concept from buildings to cities and seeks to evaluate Nearly Zero Energy Cities (nZEC): cities made up of Nearly Zero Energy Buildings (nZEB) and other installations of distributed generation to cover their energy demand by use of local renewable resources to the detriment of external resources. By using public data, we apply this model with the aim of economically evaluating the investment of six packages of energy rehabilitation and photovoltaic self-consumption in 17% of the residential buildings (37,800) in the city of Barcelona. To do this, we simulated 37 years of electricity distribution among Consumers, Producers and a hypothetical peer-to-peer community of Prosumers during the period 2014–2050 in hourly time intervals. The results indicated that the photovoltaic self-consumption and the local markets of Prosumers help to reduce primary energy consumption, the energy costs, and the CO2 emissions.

Nowadays, in many countries wind energy is responsible for a significant part of the electricity generation. For this reason, Transmission System Operators (TSOs) are now demanding the wind power plants (WPPs) to contribute with ancillary services such as frequency support. To this end, WPPs must be able to temporally increase the active power delivered into the grid to compensate consume and demand imbalances. This implies that WPPs now work below their maximum capacity to keep some power reserve to be able to inject extra power into the grid when needed. This reserve depends on the available wind power, which is directly connected with the wind speed faced by each turbine within the WPP. However, wind speed is negative affected by the wakes caused by the upstream turbines. This paper proposes a control algorithm to distribute the power contribution of each turbine seeking to minimize the wake effects and thus maximize the power reserve. The proposed algorithm is evaluated by simulations for the case of a WPP of 12 wind turbines., This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skodowska-Curie grant agreement No 675318 (INCITE).